Slavic languages have changed very little compared to the changes English was subject to.
Just figured out there is Wikipedia in Old English, you basically cannot understand anything.
This is an article about the Moon
https://ang.wikipedia.org/wiki/M%C5%8DnaCitat:
Se Mōna is þæt þe ymbgǣþ þā eorðan. Ēac cann man þæt ƿord brūcan tō hātenne gelīc tungol þe ymbgā ōðerne planētan. Hē nis sƿā grēat sƿā ǣnig þāra Sinnlicre Endebyrdnesse planētena.
Se dæg Mōnandæg is genemned tō ƿendednesse þæs Lǣdenan ƿordes lunae dies.
It has a Swedish sound to me, in fact I can more easily understand contemporary Swedish than this Old English.
There are only about 26% of Germanic words left in "English", out of that Old English is 20% and Norse perhaps 6% (Vikings conquered Britain on several occasions).
